JP2002356650A - Photocatalytic film-forming composition and photocatalytic member obtained by applying it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalytic film-forming composition which can form a photocatalytic film, on a substrate having an excellent rigidness and an excellent abrasion resistance, obtained by a low-cost wet process, and to provide a photocatalytic member having the film obtained by applying it and drying it. SOLUTION: The photocatalytic film-forming composition comprises titanium oxide which is previously surface-modified using at least a carboxylic acid, a silicone binder and a solvent. Its pH is 2-5. The titanium oxide is a crystalline titanium oxide particle whose average size is 1-100 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a composition capable of forming a titanium oxide-containing coating film used as a photocatalyst, and a method of forming the same on a surface of glass, metal, cement, wallpaper, gypsum board, stone, ceramics, resin, or the like. Related to the member provided.

[0002]

2. Description of the Related Art Photocatalytic members have functions such as antifogging, self-cleaning by rainfall, and decomposition of harmful substances. Therefore, research and development are being actively conducted as environmentally friendly functional coating materials for coatings. In the production of such a photocatalytic member, a method of forming a photocatalytic functional coating film on a base material has been mainly used in order not to impair the inherent characteristics of the member.

As a method for forming the photocatalytic coating film, there are a dry method and a wet method, but it has excellent hardness and abrasion resistance enough to withstand a wide range of use conditions while maintaining sufficient photocatalytic activity. In order to form a photocatalytic film,
There are problems with each method. A dry method typified by a sputtering method, a CVD method, a plasma method, or the like has a problem that the cost is high and a film cannot be formed depending on the material and shape of the base material.

On the other hand, in a wet method such as a sol-gel method which is low in cost and can be applied to many substrates, a method using a titanium oxide sol to which various dispersants are added, a method using a titanium oxide precursor, a method using a titanium oxide sol, Various coating film forming compositions have been proposed so far, such as a method using a mixture of a binder (hereinafter, a binder component), and any of them has a photocatalytic coating film having excellent hardness and abrasion resistance. It cannot be said that it forms.

[0005] Specifically, JP-A-2000-119 discloses a method utilizing a titanium oxide sol to which various additives are added.
According to No. 019, acidic titanium oxide sol, Ti in solution
^A pH of 5 to 10 consisting of a complexing agent added to prevent titanium oxide particles from binding to each other by aggregation of titanium oxide with ⁴⁺ ions and preventing aggregation of titanium oxide, and an alkali component added to adjust pH. The hardness of the coating film baked at 80 ° C. is about 2H or less in pencil hardness.

Further, in a method of using a mixture of a titanium oxide sol and a binder component as a main component, Japanese Patent Laid-Open No.
According to 000-273355, there is a photocatalytic paint in which β-diketone, a Ti-based or Al-based coupling agent, and a Ti alkoxide binder are combined with fine particle titanium oxide synthesized by a gas phase method. Has a pencil hardness of about 3H. Further, Japanese Unexamined Patent Application Publication No. 11-3231
No. 90 and JP-A-11-323257, there is a photocatalytic paint in which β-diketone, a Ti-based or Al-based coupling agent, and an alkoxysilane oligomer binder are combined with fine-particle titanium oxide. The pencil hardness is about 3H to 6H. Also, Japanese Unexamined Patent Application Publication No.
According to JP-A-323191, there is a photocatalytic paint in which β-diketone, a Ti-based or Al-based coupling agent, and a fluorine-based surfactant-containing ethylsilicate hydrolyzate binder are combined with fine-particle titanium oxide. The pencil hardness of the film is about 3H to 6H.

[0007]

According to the present invention, there is provided a photocatalytic coating film forming composition capable of forming a photocatalytic film having excellent hardness and abrasion resistance on a substrate surface by a low-cost wet method, and a composition comprising the same. A photocatalytic member having a coated and dried coating is provided.

[0008]

According to the present invention, in order to solve the above problems, at least one of (A) carboxylic acids belonging to
(B) titanium oxide or a precursor of titanium oxide having a Ti—O bond, the surface of which has been modified in advance using at least one kind of substance; Provided is a photocatalytic coating film-forming composition (E) having a pH of 2 to 5, comprising a system binder and (D) a solvent. Hereinafter, unless otherwise specified, (B) is referred to as titanium oxide, and (B) titanium oxide surface-modified with (A) is referred to as surface-modified titanium oxide.

When the photocatalytic coating film-forming composition is formed on a substrate and dried, a photocatalytic coating film having a very high surface hardness of 7H or more is obtained. The coating film formed from the composition of the present invention has a pencil hardness of 7H or more because the titanium oxide and the base material, and the silicon-based binder which functions to firmly bind the titanium oxide to each other, and the surface modification of the titanium oxide It may be due to the interaction of the carboxylic acid used in the process. Due to the chemical structure of the carboxylic acid, the residual hydroxyl group (-O
H) acts on the reactive functional group of the silicon-based binder,
It is considered that titanium oxide is positively incorporated as a part of the network crosslinking of the binder via the carboxylic acid. Then, it is considered that the organic structure of the carboxylic acid has an action of suppressing internal defects and shape damage. It is considered that a coating film with fewer defects and high densification and cross-linking was achieved by these actions.

In a preferred aspect of the present invention, the titanium oxide (B) has an average particle diameter of 1 to 100 nm. The average particle size of the titanium oxide is determined in consideration of the balance between the photocatalytic activity of the coating film and the mechanical strength. Titanium oxide is in the form of fine powder, and the fine particle having an average particle diameter of about 1 to 100 nm is preferable because the titanium oxide has a strong photocatalytic activity and is highly filled during coating film formation to improve hardness and wear resistance. With such a size, the scattering effect on visible light is reduced and the transparency is increased. In addition, for members such as ceramics and glass that require particularly high hardness and abrasion resistance, the particle size is preferably 30 nm or less in consideration of the balance with photocatalytic activity. Further, when it is desired to achieve high hardness and high wear resistance, the thickness is preferably 10 nm or less.

In a preferred embodiment of the present invention, the titanium oxide (B) is used in an amount of 1 to 1000 parts by weight in terms of titanium dioxide with respect to 1 part by weight of the (A) carboxylic acid for modifying the surface of the titanium oxide (B). Part. The ratio between titanium oxide and carboxylic acid is determined in consideration of the balance between the properties of the liquid such as dispersion and viscosity in the composition of the present invention and the mechanical strength such as hardness and abrasion resistance of the coating film. The ratio is preferably 1 to 1000 parts by weight of titanium oxide in terms of titanium dioxide with respect to 1 part by weight of carboxylic acid. If the amount of the carboxylic acid is too small, when a mixture of the surface-modified titanium oxide and the silicon-based binder is formed into a coating film,
The effect of improving hardness and wear resistance tends to be small. Also,
If the amount is too large, the viscosity of the surface-modified titanium oxide alone solution, the production and adjustment of the surface-modified titanium oxide and the silicon-based binder, and the mixed solution are likely to occur. Problems such as a reduction in abrasion tend to occur.

In a preferred embodiment of the present invention, the silicon-based binder (C) is used in an amount of 10 to 400 parts by weight in terms of silicon dioxide with respect to 100 parts by weight in terms of titanium dioxide. To be contained. Since the weight ratio of titanium oxide and the silicon-based binder affects the surface structure and internal structure of the coating film, it is determined in consideration of the balance between photocatalytic activity and mechanical strength such as coating film hardness and abrasion resistance. The proportion is based on 100 parts by weight of titanium oxide in terms of titanium dioxide,
Silicone binder 10 to 40 in terms of silicon dioxide
It is preferred to contain 0 parts by weight. When the proportion of the silicon-based binder exceeds 400 parts by weight in terms of silicon dioxide, the photocatalytic function is reduced because the silicon-based binder covers titanium oxide. When the proportion of the silicon-based binder is 10 parts by weight or less in terms of silicon dioxide, The adhesive strength with the material and titanium oxide is weakened, and both are poor in practicality.

[0013] In a preferred embodiment of the present invention, the total solid content concentration of the titanium oxide (B) in terms of titanium dioxide and the silicon binder (C) in terms of silicon dioxide is 20% by weight or less. The total solid content concentration is the sum of values obtained by converting titanium oxide contained in the entire composition into titanium dioxide and converting a silicon-based binder into silicon dioxide. It is determined in consideration of the balance of the characteristics and the like. The total solid concentration is calculated as titanium dioxide equivalent of titanium oxide,
In addition, it is preferable that the total solid concentration of the silicon-based binder in terms of silicon dioxide is 20% by weight or less. When the total solid content concentration is 20% by weight or less, it may be set to meet various specifications (film thickness, film forming method, etc.).
If the content is more than 10% by weight, the dispersibility of the solid in the composition becomes poor, the stability of the composition is remarkably reduced, and gelation easily occurs. On the other hand, a high concentration is not preferred because the film-forming properties and the adhesion between the film-formed body of the composition and the substrate are significantly reduced.

According to the present invention, there is provided a photocatalytic member provided with a photocatalytic coating film formed by applying the above-described photocatalytic coating film-forming composition on the surface of a substrate, and drying and curing the composition. According to the present invention, the composition of the present invention can be formed on a substrate and dried to form a coating film on the substrate. Examples of the substrate to which the composition of the present invention is applied include members having various shapes such as glass, metal, cement, wallpaper, gypsum board, stone, ceramics, and resin, and composite molded articles. When applying to these substrates, pretreatment may be performed as necessary according to the composition and the substrate.

In a preferred embodiment of the present invention, the coating obtained by drying and curing is a photocatalytic member provided with a photocatalytic coating having a surface hardness of 7H or more. According to the present invention, a coating film obtained by forming a film of the composition of the present invention on a substrate and dried has a surface hardness of 7H or more in pencil hardness, and thus can be applied to members requiring surface hardness. Examples of the substrate to which the composition of the present invention is applied include members having various shapes such as glass, metal, cement, wallpaper, gypsum board, stone, ceramics, and resin, and composite molded articles. When applying to these substrates, pretreatment may be performed as necessary according to the composition and the substrate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in order.

The carboxylic acids (A) include maleic acid, malonic acid, fumaric acid, oxalic acid, succinic acid, and other carboxylic acids having two or more carbonyl groups in one molecule, or malic acid, glycolic acid, and the like. , Lactic acid, tartaric acid,
Preferably, the chemical substance is selected from hydroxycarboxylic acids such as citric acid and gluconic acid. The chemical substance has two or more hydroxyl groups in one molecular structure. If two or more hydroxyl groups do not exist, the residual hydroxyl groups of the carboxylic acid modified on the surface of the titanium oxide are reduced and the action with the silicon-based binder is reduced, so that the coating film is highly densified,
It is considered that cross-linking is hardly achieved. Further, if the number of hydroxyl groups is too large, it is considered that problems such as production and adjustment of the surface-modified titanium oxide alone, the surface-modified titanium oxide and the silicon-based binder, and aggregation and thickening of the mixture are caused.

Regarding (B) titanium oxide having a photocatalytic action of the above composition, excited electrons and electrons jump out by irradiation with light having an energy not less than a specific value (about 3.2 eV). The holes are titanium oxides that exhibit an oxidative decomposition action of organic substances and a hydrophilic action by adsorption of water molecules, respectively. For example, crystalline titanium oxide particles, amorphous titanium oxide particles, and other titanium oxide precursors having a Ti—O bond are used. However, crystalline titanium dioxide particles are preferred. The crystalline titanium dioxide particles include anatase type, brookite type and rutile type, and particularly preferably anatase type and brookite type. Further, they may be mixed. Further, as for the amorphous titanium oxide particles, it is preferable that the crystallization is advanced by heating to improve the photocatalytic action. Further, as the titanium oxide precursor, a precursor which is polycondensed by heating and is transformed into crystalline titanium oxide, such as hydroxytitanate or organic titanate, is preferable.

In the production of the surface-modified titanium oxide, a sol in which crystalline or amorphous titanium oxide particles are dispersed in a dispersion medium is used, or a titanium oxide such as titanium alkoxide, titanyl sulfate or titanium tetrachloride is dispersed in a dispersion solvent. A method of forming a sol by mixing a precursor and performing a treatment such as neutralization, hydrolysis, deacidification treatment, or dealkalization treatment is suitably used. For example, when using titanyl sulfate as a starting material, the sol that has been hydrolyzed and filtered and washed at a temperature higher than room temperature is redispersed in a solvent, or an anion generated during hydrolysis is treated with an ion exchange resin. A method of adding an acid such as a carboxylic acid and, if necessary, an inorganic acid, and a method of further performing a hydrothermal treatment to improve the crystallinity are preferably used.
When titanium tetrachloride is used as a starting material, chlorine ions generated after hydrolysis at a temperature higher than room temperature or during hydrolysis are subjected to a dechlorination treatment such as electrodialysis, an ion exchange resin, and electrolysis to obtain chlorine. Ion concentration, p
A method of controlling H and adding a carboxylic acid, if necessary, an acid such as an inorganic acid, the hydrolysis using a carboxylic acid,
A method of controlling the chloride ion concentration and pH by dechlorination is suitably used. Further, a method of adding a carboxylic acid to the titanium oxide sol is also suitably used.

The (C) silicon-based binder of the composition functions to firmly bond the titanium oxide to the base material and the titanium oxide during the curing of the coating film and to semipermanently exhibit the photocatalytic activity of the titanium oxide. . Further, it is a binder having a pH value that can be stably mixed with the surface-modified titanium oxide. The binder of the present invention, titanium oxide and a substrate,
In addition, it is preferably an uncured siloxane polymer that has a role of firmly bonding titanium oxides to each other and has a role of semipermanently exhibiting the photocatalytic activity of the titanium oxide, and is formulated to have a pH value that can be stably formulated with the surface-modified titanium oxide sol. .
The uncured siloxane polymer has a general formula R1 (n1) SiX (4-n1) (1) wherein n1 is an integer of 0 or 1. R1 has 1 to 18 carbon atoms.
Is a monovalent organic group in which one carbon atom is bonded to a silicon atom. X is chlorine, bromine, or an alkoxy group having 1 to 4 carbon atoms. A mixture of a hydrolyzable trifunctional silicon compound and a hydrolyzable tetrafunctional silicon compound represented by the following) or a compound obtained by subjecting a hydrolyzable tetrafunctional silicon compound to hydrolysis and polycondensation under acidic conditions is preferable. More preferably, it is an uncured siloxane polymer obtained by hydrolyzing and polycondensing a hydrolyzable tetrafunctional silicon compound. Also preferably, a general formula Si (n2) O (n2-1) OR2 (2n2 + 2) (2) (where n2 is an integer of 2 to 6. R2 is an alkoxy group having 1 to 4 carbon atoms. Hydrolyzable 4 represented by
It is an uncured siloxane polymer obtained by subjecting a condensation polymer of a functional silicon compound to hydrolysis and condensation polymerization under acidic conditions. Further, the general formula: M (n3) O. (n4) SiO2 (3) (wherein, M is an element belonging to alkali metals. N3 is a numerical value determined by the valence of M. n4 is a numerical value of 1 to 8. M is Fr, Cs, Rb, K, Na, L
neutralizing a silicon compound containing an element belonging to at least one or more alkali metals such as i, an alkali metal silicate solution (hereinafter, referred to as an alkali silicate),
It may be an acidic uncured siloxane polymer obtained by performing a suitably used method such as alkali elimination by electrodialysis, ion exchange resin, or electrolysis. Further, a product obtained by adding silica fine particles to the uncured siloxane polymer, or a product obtained by reacting a silicon compound represented by the general formula (1), the general formula (2), or the general formula (3) with silica fine particles is used. It may be used.

In the silicon compound represented by the general formula (1), the hydrolyzable trifunctional silicon compound includes methyltrichlorosilane, methyltribromosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane. , Methyltri-t-butoxysilane, ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, vinyltrichlorosilane, vinyltribromosilane, vinyltrimethoxysilane, vinyltriethoxysilane Examples thereof include silane, trichlorohydrosilane, tribromohydrosilane, trimethoxyhydrosilane, and triethoxyhydrosilane. Examples of the hydrolyzable tetrafunctional silicon compound include tetrachlorosilane, tetrabromosilane, tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane,
There is dimethoxydiethoxysilane. Preferred are tetramethoxysilane and tetraethoxysilane, which are easily available and easy to obtain a high hardness when dried. In addition, the general formula (2)
Examples of the silicon compound represented by are methyl silicate 51, which is an average trimer condensation product of tetramethoxysilane, and an average pentamer condensation product of tetraethoxysilane, which are easily available and easily obtain a high hardness body when dried. Ethyl silicate 40 is preferred. Examples of the silicon compound represented by the general formula (3) include an aqueous solution of sodium silicate No. 1, an aqueous solution of sodium silicate No. 3, an aqueous solution of sodium silicate No. 4, an aqueous solution of sodium silicate No. 1, an aqueous solution of potassium silicate 1K, B potassium silicate aqueous solution, various lithium silicate aqueous solutions and the like. Other examples of the alkali silicate include ammonium silicate in which an alkali metal is reduced as much as possible and stabilized with organic amines (short-chain amines such as formaldehyde, ethylamine, and ethanolamine).

The (C) silicone binder of the present invention comprises:
The hydrolyzable tetrafunctional silicon compound represented by the general formula (1) or the polycondensate of the hydrolyzable tetrafunctional silicon compound represented by the general formula (2) is not hydrolyzed and polycondensed under acidic conditions. More preferably, it is a cured siloxane polymer.

In the hydrolysis of the hydrolyzable silicon compound, either an acid or an alkali can be used as a catalyst. However, considering the stability of the hydrolyzed binder component, the surface-treated titanium oxide sol, and the mixture thereof, contact with water occurs. Then, (E) it is desirable to show acidity with a pH of 2 to 5. Particularly preferred are acidic hydrogen halides, carboxylic acids, sulfonic acids, acidic or weakly acidic inorganic salts, and solid acids such as ion exchange resins. Preferable examples include hydrogen fluoride, hydrochloric acid, nitric acid, sulfuric acid; organic acids represented by acetic acid and maleic acid; methylsulfonic acid; and cation exchange resins having a sulfonic acid group or a carboxylic acid group on the surface. . The amount of the hydrolysis catalyst is preferably in the range of 0.001 to 5 mol per 1 mol of the hydrolyzable group on the silicon atom. In addition, when it is on the strongly acidic side of pH 2 or less or on the neutral side of pH 5 or more, the hydrolyzed binder component becomes unstable and easily gelates.

The amount of water used for the hydrolysis is determined by considering the curability of the coating film, the mechanical strength and appearance of the obtained coating film, the stability of the liquid such as mixing with a surface-treated titanium oxide sol, and the like. 0.001 to 1 mol of the above hydrolyzable group
It is preferably in the range of 500 moles, preferably 0.05 to 100 moles. For the hydrolysis reaction, polar solvents such as alcohols, ketones and esters, or toluene,
It is preferable to use a non-polar solvent such as hexane as the solvent. These solvents may be used for the solvent (D) of the present invention. When halogenosilane is used as a raw material, it is necessary to sufficiently wash with water after hydrolysis to remove halogen components.

The molecular weight of the siloxane compound composed of the uncured siloxane polymer formed by partially hydrolyzing and polycondensing the hydrolyzable silicon compound monomer in this way affects the physical properties of the coating film. If the molecular weight is too small, defects and shape damage are likely to occur during drying and curing, and it is considered that the coating film hardness and abrasion resistance are reduced. A film having a higher molecular weight can form a film having good transparency, gloss and smoothness. The siloxane compound has a number average molecular weight of 80 determined by GPC (gel filtration chromatography) using polystyrene as a standard substance.
Those having a molecular weight of up to 20,000 are preferred.

The surface-modified titanium oxide and the silicon-based binder can be appropriately mixed. For example, a predetermined amount of the aqueous dispersion of the surface-modified titanium oxide under an acidic condition may be mixed with 10 to 5 times.
While maintaining the liquid temperature at 0 ° C., the weighed silicon-based binder is added dropwise thereto over a certain period of time. After dropping,
The reaction is carried out with stirring for 5 hours to prepare a composition liquid. The silicon-based binder is preferably an uncured siloxane polymer obtained by previously subjecting the hydrolyzable silicon compound to hydrolysis and polycondensation under pH adjustment, and then mixing this with a surface-modified titanium oxide sol with stirring. Can be obtained. Further, a method in which a hydrolyzable silicon compound and a hydrolysis catalyst are simultaneously added to a surface-modified titanium oxide sol, and a method in which hydrolysis is promoted by utilizing an acid component present in a surface-modified titanium oxide dispersion are suitably used. . In the case of using an alkali silicate, a method in which the pH is adjusted in advance by the above-described method and the mixture is prepared is preferably used.

The solvent (D) of the composition is a substance capable of uniformly dispersing the surface-modified titanium oxide and the silicon-based binder, which are film-forming elements. For example, water or lower alcohols such as methanol, ethanol, isopropyl alcohol, n-propanol, n-butanol and isobutanol, or ketones such as methyl ethyl ketone (MEK) and methyl isobutyl ketone (M
IBK). Preferably, it is water or the lower alcohols. Also, the diluent for diluting the composition,
Water and organic solvents can be used. Alcohols, ketones, esters and ethers are suitable as organic solvents.

The pH of the composition (E) is 2-5.
The pH range is advantageous for improving the stability when the components of the film-forming element are produced and prepared. If it is on the strongly acidic side of pH 2 or less or on the neutral side of pH 5 or more, the silicon-based binder becomes unstable.

In the present invention, a coating composition comprising (A) titanium oxide having photocatalytic activity and (C) a silicon-based binder which has been surface-modified in advance using at least one or more substances belonging to carboxylic acids. By drying and curing, a photocatalytic coating film having excellent hardness and abrasion resistance was realized. The mechanism by which the coating film obtained by the photocatalytic coating film-forming composition of the present invention has high hardness and high abrasion resistance is not necessarily clear. However, the effect of achieving high hardness and high abrasion resistance is the weakness of the bonding interface between titanium oxide and the binder, which was a weak point in the wet method in which the conventional inorganic acid-dispersed titanium oxide sol was mixed with the binder during drying. This is considered to be because the action of strengthening and, in addition, the action of reducing internal defects and shape damage during drying of the photocatalytic coating film forming composition can be expected from the chemical structure of the carboxylic acid. In addition, it is considered that titanium oxide alone or a mixture with a binder component also has an effect as a dispersant for reducing aggregation and precipitation of titanium oxide.

The effect of strengthening the weakness of the bonding interface between the titanium oxide and the binder is as follows: the residual hydroxyl group (-OH) of the carboxylic acid coating the surface of the titanium oxide particles at the time of drying and curing the coating film is a function of the silicon-based binder. By acting on the reactive functional group, it is considered that titanium oxide is positively incorporated as a part of the network crosslinking of the binder via the carboxylic acid. Therefore, it is considered that a high degree of densification and cross-linking were achieved even in a coating film processed by low-temperature drying.

Further, when the composition of the present invention is dried,
As an action of reducing internal defects and shape damage, the presence of a carboxylic acid having an organic structure imparts flexibility to the composition, and forms a coating film with less defects during drying and curing. Such a function as a kind of molding aid can be considered. Therefore, it is considered that a highly densified coating film having fewer defects was realized.

The function as the dispersant is to reduce unevenness in film formation at the time of forming a coating film, poor mechanical strength and poor appearance due to aggregation and precipitation of titanium oxide. Conceivable. A photocatalytic coating film made of titanium oxide and a silicon-based binder not subjected to surface modification, for which the above effects cannot be expected, cannot achieve high hardness and high wear resistance.

In the present invention, it is more preferable that the present invention has the various features described above. Further, various additives may be appropriately added as desired. Specific examples include curing catalysts, various surfactants, thickeners, dispersants, foaming agents, silane or titanium coupling agents, and dyes.

In the present invention, the composition is applied to a substrate, dried, and optionally heated and baked to form a coating. The heating temperature is not limited, but may be from 100 ° C to 8 ° C.
00 ° C is preferred. In addition, a method suitable for the shape and size of the substrate to be coated is appropriately used as the coating method. For example, there are a brush coating, a spray method, a bar coater method, an applicator method, a spin coating method, a dipping method, a curtain wall method and the like. In general, it is preferable to set the solid concentration of the composition to be lower as the amount of the film attached to the substrate is larger.

In the film formation of the present invention, the film hardness, abrasion resistance,
In order to express photocatalytic activity and appearance in a well-balanced manner,
An important factor is not only the weight ratio of the oxide values of titanium dioxide and silicon dioxide but also the thickness of the coating film.
In the composition of the present invention, the film thickness is preferably from 10 to 1000 nm. In a specification in which transparency is also important, 10 to 300 nm is a preferable film thickness.

In the present invention, a photocatalytic material having a surface hardness of 7H or more and abrasion resistance, which is superior to the conventional titanium oxide formed by the same acid or alkali and formed under the same sintering conditions even at a low sintering temperature. A coating can be formed. Therefore, to promote the curability of the coating film, or to always reduce the time required for heat treatment at a higher temperature for the purpose of shortening the curing time of the coating film, for example, the properties of the substrate are impaired,
Problems such as cost can be reduced. Further, a photocatalytic coating film having excellent hardness and abrasion resistance can be formed even on a member such as a building that cannot be subjected to heat treatment at a high temperature.

When a thin film is formed on the member surface by the above method,
The surface of the member exhibits hydrophilicity and decomposability in response to photoexcitation of titanium oxide, which is an optical semiconductor. Here, the illuminance of the excitation light may be 0.001 mW / cm2 or more, and is preferably 0.01 mW / cm2 or more, in order to highly hydrophilize the substrate surface by optical excitation of the optical semiconductor. .
More preferably, it is 1 mW / cm2 or more. As a light source,
Sunlight, indoor lighting, fluorescent lamps, mercury lamps, incandescent lamps, xenon lamps, high-pressure sodium lamps, metal halide lamps, BLB lamps, germicidal lamps and the like can be suitably used. However, when a thin film having a thickness of 100 nm or less is used, it is preferable that the thin film contains a large amount of short-wavelength light having a good absorbency of about 250 to 350 nm (preferably about 300 to 350 nm).

As the substrate on which the composition of the present invention is applied,
Members having various shapes, such as glass, metal, cement, wallpaper, gypsum board, stone, ceramics, and resin, and composite molded articles are conceivable. When applying to these substrates, it is necessary to perform a pretreatment suitable for the substrate as well as the composition.

The substrate to which the present invention can be applied includes anti-fog,
When a drip-proof effect is expected, it is a transparent member, and glass, plastic, or the like can be suitably used for the material. Speaking of applicable base materials, mirrors such as rearview mirrors for vehicles, mirrors for bathrooms, mirrors for toilets, dental mirrors, road mirrors; spectacle lenses, optical lenses, illumination lenses, semiconductor lenses Lenses such as copier lenses, rear view camera lenses for vehicles; prisms; windows of buildings and towers; automobiles, railway vehicles, aircraft, ships, submersibles, snowmobiles, lowway gondola, amusement parks Gondolas, vehicle windows such as spaceships; cars, motorbikes, railcars, aircraft, ships, submersibles, snowmobiles, snowmobiles, lowway gondola, amusement park gondola, space Windshields for vehicles such as ships; protective goggles, sports goggles, protective mask shields, sports mask seals
Helmet shield, glass of frozen food display case, glass of warm food display case such as Chinese steamed bun; cover of measuring instrument, cover of camera lens for rear view confirmation for vehicle, laser Converging lenses for dental treatment devices, laser covers such as inter-vehicle distance sensors, covers for light detection sensors, covers for infrared sensors, filters for cameras, and for attaching to the surface of the article. Films, sheets, seals, patches and the like can be mentioned.